The compound bow has become popular among archers after the development initiated primarily by Holless W. Allen who was granted U.S. Pat. No. 3,486,495 on Dec. 30, 1969. This patent discloses a bowstring passing over a first cam pulley which is eccentrically mounted at the distal end of bow limbs. As the bowstring is drawn, the bowstring cable unwraps from the cam pulley. However, a second pulley is mounted adjacent to and turns with the first pulley and a tension cable on this second pulley wraps up on the second pulley as the bowstring is drawn. The tension pulley has each end anchored at the distal end of a bow, usually on the axle mounting the pulleys, and the tension pulley extends from each anchor point at one end to the second pulley at the other end.
Archers' bows may have a bowstring pull varying all the way from 15 pounds to 100 pounds. When the rating gets above 35 pounds, it requires a rather strong person to pull the bowstring back to the release position and to hold the arrow in this position while it is being aimed. With the improved bow construction (devised by Allen), the pull on the bowstring is high at the beginning of the draw but the arm at this point is able to exert a maximum force. As the draw progresses a little beyond mid-point, there is an overcenter action on eccentric pulleys which decreases the draw force needed to maintain the bowstring in drawn position without decreasing the energy stored in the limbs of the bow. Thus, at full drawn, it is relatively easy to hold the arrow and bowstring and much easier to perfect the aiming technique and the proper finger release.
Modern bows are usually fashioned with a rigid handle portion centrally located and flexing bow limbs mounted at the proximal ends on each end of the handle portion. The pulleys are mounted on the distal ends of the bow limbs which are usually bifurcate and transfixed by the axle on which the pulleys rotate. The flexing bow limbs are formed as composite laminations of special wood or solid fiberglass and are usually well matched as to flexibility. However, an imbalance can be caused by improper assembly of the bow components or because of unequal stretch characteristics of the cables or bowstring. This imbalance is undesirable and various correctional devices have been proposed.
A U.S. patent to Darlington 3,987,777 (1976) shows supplemental pulleys on the bow handle which would allow adjustment of one or both ends to achieve what is referred to as tuning. A U.S. patent to Simonds 4,440,142 (1984) illustrates a means of anchoring the tension or timing pulleys utilizing a separate pulley sheave mounted on a looped bridle cable at each end of the bow. The sheave has a plurality of notches with varying dimension to adjust the anchor point of the tension cable.
The present invention contemplates the use of an anchor disc mounted directly on the pulley axle to avoid the use of the complicated bridle assembly and simplify the means of adjusting tension cable lengths for tuning and draw lengths.
Objects and features of the invention will be evident in the following description and claims in which the principles of the invention are set forth together with details to permit persons skilled in the art to practice the invention, all in connection with the best mode presently contemplated for the invention.